The invention relates to a fan impeller comprising a hub and blades extending radially outward from the hub, the blades having a flattened airfoil profile cross section with a leading edge and a trailing edge between which a chord is defined.
Impellers such as this are used in particular for cooling the engine that propels motor vehicles, the impeller producing an air flow through a heat exchanger, namely the radiator used to cool the propulsion engine.
The hub of the impeller, also known as the “bowl”, can be fitted securely onto the shaft of a motor which may be an electric motor operated by control electronics.
The expression “flattened cross section” is intended here to denote the flat closed curve obtained by cutting through the blade on a surface that is a cylinder of revolution about the axis of the impeller and laying this cylindrical surface out flat. The chord is then defined as the length of straight line connecting the leading edge and the trailing edge.
When an impeller such as this is used for cooling a motor vehicle engine, it is positioned either in front of or behind the radiator used to cool the engine.
Designing impellers such as this in practice presents numerous problems when seeking to improve their aeraulic and acoustic performance.
Fan impellers are generally produced by molding a plastic. In order to reduce manufacturing costs, it is commonplace for the impeller blades to be produced in the form of an airfoil with the smallest possible thickness.
Furthermore, most known fan impellers have a fairly substantial axial depth in order to reduce the loads applied to the blades and therefore the noise generated by the fan.
Thin-blade impellers are compatible with reducing the axial size but on the other hand are better suited to cooling motor vehicle engines where the impeller lies a significant distance (typically several centimeters) away from the cooling radiator matrix.
Given the fact that the space available in the engine compartment of motor vehicles is often very limited, it is desirable not only to have impellers that occupy a small amount of space in the axial direction, but also to be able to reduce the distance between the impeller and the cooling radiator matrix.
Now, thin-blade impellers, as taught for example by FR-A-2 781 843 experience a drop in aeraulic and acoustic performance when situated close to a heat exchanger matrix, for example a cooling radiator. This drop in performance is due chiefly to the disturbances caused by the great deal of turbulence resulting from the heat exchangers. The expression “close” is intended here to denote a distance typically of the order of 1 cm.